Synthetic fibers fabricated primarily from polyamide, polyester, vinylon, polyolefin, etc. are now used as industrial synthetic fibers for fishery, agricultural, and construction uses, because improved tenacity and weatherproof are demanded in such applications. For lack of self-degradability, however, such synthetic fibers, if left undisposed at hills and fields and in the sea after use, offer problems that not only are they detrimental to landscapes, but also they cling to birds, oceanic life, divers or the like, killing them or to marine engines, leading to shipwrecks. These problems may be solved if used-up synthetic fibers are disposed by incineration, landfilling or regeneration; however, they are still left undisposed at hills and fields or in the sea because much labor and cost are taken for such disposals. To provide a solution to those problems, the use of synthetic fibers fabricated from biodegradable polymers is now taken up for consideration, and so a variety of biodegradable synthetic fibers are under development. In particular, efforts are focused on making fibriform lactic acid polymers because they are biodegradable polymers from which articles having practical mechanical properties and heat resistance can be formed at relatively low costs. The present invention relates to improvements in an agent and method for treating biodegradable synthetic yarns fabricated from lactic acid polymers.
For agents for treating biodegradable synthetic yarns fabricated from lactic acid polymers, there have so far been proposed (1) an agent comprising water, ethylene glycol, polyethylene glycol, silicone oil, etc. (JP-A's 10-110332 and 2000-154425), (2) an agent in which mineral oil lubricants are used as a lubricant (JP-A 2000-192370), and (3) an agent comprising an anionic surfactant such as potassium laurylphosphate, an cationic surfactant such as a quaternary ammonium salt, a nonionic surfactant such as an aliphatic higher alcohol and a higher fatty acid ethylene oxide adduct, a polyalkylene glycol such as polyethylene glycol, block copolymer of polyethylene glycol and polypropylene glycol, and a silicone oil such as dimethylsiloxane, polyether-modified silicone oil and higher alcohol-modified silicone (JP-A's 7-118922 and 7-126970). However, problems with those prior art agents are that they cannot impart any sufficient lubricity, cohesion or the like to biodegradable synthetic yarns fabricated from lactic acid polymers, and so fuzzing and yarn breakage are often found at every step from spinning to down-stream step, especially at a false twisting step. These factors, combined with poor bulkiness, then interact one another, resulting in a failure in producing yarns having satisfactory mechanical properties in a stable fashion.
An object of the present invention is to provide an agent and method for treating biodegradable synthetic yarns fabricated from a polymer comprising lactic acid as a main component (hereinafter called the lactic acid polymer), which enable improved lubricity, cohesion, etc. to be so imparted to the biodegradable synthetic yarns that the yarns can be prevented from fuzzing and breaking at every step from spinning to down-stream step, especially at a false twisting step and improved in terms of bulkiness, providing yarns having improved mechanical properties in a stable manner.
The inventors have now found that for treating biodegradable synthetic yarns fabricated from the lactic acid polymer it is reasonably preferable to use an agent comprising a specific functional agent at a given proportion and having a friction coefficient in a predetermined range.